In the last month or so i've been reading up a lot about evolution, and i've watched videos, and i'm currently reading "the greatest show on earth" and i've started wondering about something...

in the book, Dawkins speaks several times about species being separated by "islands" (an island in the sense of a livable area surrounded by inhospitable areas - a lake is a island for fishes, surrounded by inhospitable land, etc) who then evolve in different directions and if they remain separated long enough, they become two different species who would only be able to produce infertile offsprings or even completely incompatible, so they're classed as different species at that point. This has even been actually observed in nature, it's not just something they figured out from fossils (i don't have the book right now to check and give exemples, sorry)

anyway, about humans... the way i understand it (correct me if i'm wrong), there has been two "exodus" from africa, and it's in the second one that it was "fully" evolved (well evolution doesn't really stop but anyway, you get what i mean) homo sapiens that went gradually everywhere else in the world. From what i understand, they encountered different species of humans from the first exodus, for exemple the neandertals, and they eventually drove those different species of human to extinction, so that today only the homo sapien remains...

So i've wondered... if before, humans in different locations evolved differently than those who remained in Africa, why was it different the 2nd time? Sure, humans in different locations changed a little bit; lighter skin color, etc. But that's just different "races", we're still all the same species.. how come?

Was it because at that point human quickly (in evolutionary terms) became advanced enough to be in contact with other tribes/civilisations, so that there were no real "barriers" anymore to allow speciation? But they didn't mingle that much did they?

So i've wondered... if before, humans in different locations evolved differently than those who remained in Africa, why was it different the 2nd time? Sure, humans in different locations changed a little bit; lighter skin color, etc. But that's just different "races", we're still all the same species.. how come?

Was it because at that point human quickly (in evolutionary terms) became advanced enough to be in contact with other tribes/civilisations, so that there were no real "barriers" anymore to allow speciation? But they didn't mingle that much did they?

All modern humans have a common ancestor who was alive relatively recently, in evolutionary terms. The earliest suggestion I've seen is that our common ancestor lived around 70,000 years ago, but I've seen statisticians posit that (with issues like the hemisphere divide aside) we could statistically all have a common ancestor from only 2000 to 5000 years ago. We haven't had the time necessary for major speciation.

Plus, we tend to spread our genes around and mix them up a lot. Humans often have children with people outside their cultural in-group (if we didn't, then cultural elites wouldn't feel the need to put so much effort into enforcing social prohibitions against it). Our ancestors traveled quite a lot, too. Traveling most likely cut down a great deal post-agriculture, but before that populations migrated.

Plus, you have to remember that several species of humans who lived contemporaneously with our ancestors all died out. We don't see the effect of past speciation today because the other branches of the tree were cut off.

So i've wondered... if before, humans in different locations evolved differently than those who remained in Africa, why was it different the 2nd time? Sure, humans in different locations changed a little bit; lighter skin color, etc. But that's just different "races", we're still all the same species.. how come?

Was it because at that point human quickly (in evolutionary terms) became advanced enough to be in contact with other tribes/civilisations, so that there were no real "barriers" anymore to allow speciation? But they didn't mingle that much did they?

All modern humans have a common ancestor who was alive relatively recently, in evolutionary terms. The earliest suggestion I've seen is that our common ancestor lived around 70,000 years ago, but I've seen statisticians posit that (with issues like the hemisphere divide aside) we could statistically all have a common ancestor from only 2000 to 5000 years ago. We haven't had the time necessary for major speciation.

Plus, we tend to spread our genes around and mix them up a lot. Humans often have children with people outside their cultural in-group (if we didn't, then cultural elites wouldn't feel the need to put so much effort into enforcing social prohibitions against it). Our ancestors traveled quite a lot, too. Traveling most likely cut down a great deal post-agriculture, but before that populations migrated.

Plus, you have to remember that several species of humans who lived contemporaneously with our ancestors all died out. We don't see the effect of past speciation today because the other branches of the tree were cut off.

ah ok, i was under the impression that our common ancestor lived quite a longer time ago than that ..i mean homo sapiens leaving Africa... are you saying this happened multiple times (more than like 2 times), each times replacing populations in other places? ...but i don't think it can be as recent at 5000 years ago, i mean just thinking of native americans, they were there for more than just 5000 years.

hmm... i've read the articles and for some reason i keep thinking things are more complicated than those mathematical calculations... i'm not good enough at math and i don't know enough about human history to explain why i feel like there's something not right about those calculations but... i dunno something feels off about them..

maybe there's something i don't understand about it. I mean, okay, maybe we all have a *common* ancestor from such recent times but, surely, there are people with ancestors that go further back? And it's just that those ancestors aren't also the ancestors of all other people alive today?

maybe there's something i don't understand about it. I mean, okay, maybe we all have a *common* ancestor from such recent times but, surely, there are people with ancestors that go further back? And it's just that those ancestors aren't also the ancestors of all other people alive today?

When we refer to something as a common ancestor we have to be careful here. I'm not affluent in the specifics of evolutionary biology such as the names of the different species but I do understand the theory of evolution.

This is actually one the most talked about issues and least understood ones at the same time, by non-scientists anyways. You have to keep in mind that evolution occurs because there is imperfect replication of the genes whenever they are made as gametes. Such imperfections is what allowed us humans to look like what we look like today. If this replication process was perfect then we surely would have died off as a whole and no animal would even be seen on this planet to this day.

Now that's out of the way, when we refer to common ancestor we have to place a frame of reference on it. This is not an absolute term as you can imagine but has to carry context.

Now take a look at the phylogenetic tree on the right, pay no attention to the tree on the left. But as you can already probably see there are a lot of points on this tree that could be called common ancestors to the species. Three such examples are (X), (A), (Z). This is self explanatory but I can take that you can see that (B) and (C) share a common ancestor (X) and (B) (C) and (D) share a common ancestor of (Z).

maybe there's something i don't understand about it. I mean, okay, maybe we all have a *common* ancestor from such recent times but, surely, there are people with ancestors that go further back? And it's just that those ancestors aren't also the ancestors of all other people alive today?

When we refer to something as a common ancestor we have to be careful here. I'm not affluent in the specifics of evolutionary biology such as the names of the different species but I do understand the theory of evolution.

This is actually one the most talked about issues and least understood ones at the same time, by non-scientists anyways. You have to keep in mind that evolution occurs because there is imperfect replication of the genes whenever they are made as gametes. Such imperfections is what allowed us humans to look like what we look like today. If this replication process was perfect then we surely would have died off as a whole and no animal would even be seen on this planet to this day.

Now that's out of the way, when we refer to common ancestor we have to place a frame of reference on it. This is not an absolute term as you can imagine but has to carry context.

Now take a look at the phylogenetic tree on the right, pay no attention to the tree on the left. But as you can already probably see there are a lot of points on this tree that could be called common ancestors to the species. Three such examples are (X), (A), (Z). This is self explanatory but I can take that you can see that (B) and (C) share a common ancestor (X) and (B) (C) and (D) share a common ancestor of (Z).

I hope this clears up the common ancestor thing for you.

hmm, ok but we're talking about homo sapians here tho ^^; and why there wasn't speciation again (because, like, pre-humans not sure what kind, but let's pretend homo erectus, had left Africa before but they didn't survive when Homo sapian came and took over) when they (homo sapian) left Africa and populated the rest of the world... and someone was saying that we don't have to go further back than like 5000 years to find a person who would be a common ancestor to every human alive today. I'm not sure about that but anyway.

i mean, from what i understood before someone posted that, is that the common ancestor of humans and chimps is some kind of ape that was not human and not chimp.. that was wayyyyy more than 5000 years ago and yet one of those ape creature is still the common ancestor of all humans today right? So how does this math logic work around that, saying that we can't go back further than that 5000 or so years? It doesn't make any sense!! gonk

Either you've misheard what someone said about the last common ancestor of all living people (not people and chimps), or whoever told you that got it wrong.
Either way, you'd have to go much farther back to find the last common ancestor of all living people, and even farther back to find the last common ancestor between people and chimps.

We're not worried about oldest common ancestor, but the youngest. By saying "we had a common ancestor 5000 years ago", that means that we are all linked by one person who lived 5000 years ago, and any splitting that could have occurred within the species called "human" would have had to happen after that one person.
Sure, there were common ancestors before that person, but all of the branches that occurred before that last common ancestor are either not considered humans, i.e. apes and such, or were killed off.

but anyway, can someone explain again to me, why this is related to why
humans didn't ...urrr, speciate... i mean when homosapians spread out of Africa, like i said they weren't the first to do that, other pre-humans had done it before and did ..speciate (is that even a word?).. so i was wondering why it didn't happen again...

i'm pretty sure i'm supposed to have understood why by now with what people said already in the thread but if someone could spell it out for me in a simple (but detailed, if possible?) way i'd be really grateful sweatdrop

We're not worried about oldest common ancestor, but the youngest. By saying "we had a common ancestor 5000 years ago", that means that we are all linked by one person who lived 5000 years ago, and any splitting that could have occurred within the species called "human" would have had to happen after that one person.
Sure, there were common ancestors before that person, but all of the branches that occurred before that last common ancestor are either not considered humans, i.e. apes and such, or were killed off.

i just re-read carefully what you said and it answers my questions in the last post i made lol. Thanks

We didn't even from Neanderthals, who already had a lot of evolutionary changes, such as specifically deigned hands, shoulders, even waists for being strong with spears and whatnot, and who spread out everywhere.

Humans left Africa only a little while ago, say 40,000 years, but it's not that big of an issue.

We didn't even from Neanderthals, who already had a lot of evolutionary changes, such as specifically deigned hands, shoulders, even waists for being strong with spears and whatnot, and who spread out everywhere.

Humans left Africa only a little while ago, say 40,000 years, but it's not that big of an issue.

"we didn't even from neandertals"...? i guess you meant to write "we didn't evolve from neandertals" .. thanks but i knew that already. I also knew about homosapians leaving Africa later... this whole topic is about that... sweatdrop